(a–c) Schematic illustration of the binding characteristics of the protein-protein or protein-lipid interaction modules expressed by adapter proteins. (a) In general, SH2 and PTB domains bind to phosphorylated TBSMs, whose binding specificities are determined by the amino acids surrounding the core tyrosine (C-terminal in case of PTB domains, N-terminal in case of SH2 domains). (b) SH3 domains constitutively interact with proline-rich regions. (c) PH domains bind to phospholipids. (d) Schematic presentation of a selection of adapter proteins involved in proximal TCR signaling.